1. Field of the Invention
This invention relates to a displacement detecting mechanism for the reflecting surface of a deformable mirror which is provided with a flexible thin film having the reflecting surface and an upper electrode, deformed by electrostatic attraction, and a control electrode located opposite to the flexible thin film, and is constructed so that a voltage applied to the control electrode is controlled and thereby the reflecting surface can be properly deformed.
2. Description of Related Art
The deformable mirror of this type, disclosed in Japanese Patent Preliminary Publication No. Hie 2-101402, can be fabricated at low cost, with a high degree of accuracy, and in microminiaturization by applying a so-called MEMS (micro electro-mechanical system) technique which utilizes a semiconductor manufacturing technique. Thus, it is expected that the deformable mirror is applied to a minute optical system used in microoptics, such as an optical pickup, and to a small-sized portable device.
In such a deformable mirror whose shape is changed by the electrostatic attraction, the amount of change thereof is governed by the balance between the electrostatic attraction exerted between both electrodes and the tension of a flexible thin film. In order to change the deformable mirror to an optimum shape, it is necessary to control a high voltage (compared with an ordinary IC device) so that it remains stable over a wide range. In particular, for the power source where the deformable mirror is applied to a microminiature device, only a low-capacity and -voltage power source like a battery cell is available in most cases. Although it can be easily realized to derive a high-voltage power source from such a low-capacity and -voltage power source because of compactness of a voltage changing element in a piezoelectric transformer, it is very difficult to control the high voltage with stability and high accuracy, in such a boosting way, over a wide range.